A fuel cell typically comprises a pair of catalyst/electrodes and an ion-transporting electrolyte sandwiched between the catalyst/electrodes. Each catalyst/electrode, for example, may be a catalyst layer over which an electrode layer extends. Alternately, each may comprise an electrode layer impregnated with a catalyst.
One catalyst/electrode may serve as a reactive or catalytic site for oxidizing a fuel such as hydrogen (H2), methanol (CH3OH), or other hydrocarbon, while the other serves as a catalytic site for reducing a reactant, typically, air or pure oxygen (O2). The electrolyte is typically a proton exchange media (PEM) that blocks the flow of electrons while conducting positively charged ions such as hydrogen ions.
The oxidation-reduction reactions at the respective catalytic sites thus result in a flow of electrons that are blocked by the PEM but are carried by a circuit connected to the fuel cell. Corresponding hydrogen protons migrate through the electrolyte. Accordingly, through the electrochemical reactions of the fuel or anodic reactant (e.g., H2 or CH3OH) with the cathodic reactant (e.g., air or O2), the fuel cell becomes a source for electrical power.
The anodic and cathodic reactants may be carried in channels. Conventional fuel cells typically rely on channels that have been formed in a substrate for carrying the reactants. A frequently used substrate is silicon. U.S. Published Patent Application 2002/0122972 to Klitsner et al., for example, discloses a plurality of reactant channels formed in a pair of silicon substrates. One of the pair of substrates is adjacent a single anodic catalyst/electrode layer and the other is adjacent a single cathodic catalyst/electrode layer. A single layer comprising an electrolyte separates the two catalyst/electrode layers.
U.S. Published Patent Application 2002/0006539 to Kubota et al. similarly discloses a pair of catalyst/electrode layers that sandwich an electrolyte. An anodic reactant is carried in channels formed in a silicon substrate adjacent one of the catalyst/electrode layers, and a cathodic reactant is carried in channels formed in another silicon substrate adjacent the other catalyst/electrode layer.
Forming channels in a substrate, such as silicon, can add to the cost of manufacturing a fuel cell. Additionally, the formation of channels should desirably not result in removal of so much silicon that the structural integrity of the substrate is impaired. Conversely, though, if the number and/or size of the channels are limited for the sake of maintaining the structural integrity of the substrate, the surface area needed to facilitate the oxidation-reduction reactions will accordingly be limited. This trade-off between structural integrity and reaction surface requirements is a particularly important consideration in making fuel cells that are sufficiently small, that is, microfuel cells, to be successfully used for powering various types of electronic devices.